When drilling wells into earth formations such as unconsolidated sandstone reservoirs for extraction of oil and gas, some means of filtering sand out of the fluid as it is drawn from the reservoir is required in order to obtain high production rates from such reservoirs. Different types of screens and filters have been applied for this purpose.
Screens may be used as filters by sizing the screen to block the flow of particles larger than a given size. Traditionally, a sieve analysis is performed on the formation sand prior to completion of the well and the formation sand particle size range is determined. A filter screen size is chosen which will block the largest e.g. fifty percent of the formation sand particle sizes.
Such screens are known from U.S. Pat. No. 5,624,560 describing a woven wire mesh arranged over a supporting body such as a metal perforated tube. Screens of sintered material for the purpose of removing sand particles from fluids in a well bore are known from US 2004/0050217 A1.
However, one problem is that these filters, such as wire wrapped steel screens, are subject to high erosion rates because the fluid flow is effectively straight through the filter material. The sand particles will exert an excessive wear on the filter material, which is often metal e.g. hardened steel.
Another problem is that the available inflow area for such filters is typically only below 10 percent of the total filter surface area, which greatly limits the maximum flow rate available from the well. Furthermore, particles will often plug openings or part of an opening in the filter material, such that the inflow area is further reduced.